Registration calculation between three-dimensional (3d) scans based on two-dimensional (2d) scan data from a 3d scanner

ABSTRACT

A method for measuring and registering three-dimensional (3D) by measuring 3D coordinates with a 3D scanner in a first registration position, measuring two-dimensional (2D) coordinates with the 3D scanner by projecting a beam of light in plane onto the object while the 3D scanner moves from the first registration position to a second registration position, measuring 3D coordinates with the 3D scanner at the second registration position, and determining a correspondence among targets in the first and second registration positions while the 3D scanner moves between the second and third registration positions.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 14/559,311, filed Dec. 3, 2014, which claims thebenefit of International Patent Application No. PCT/IB2013/003082, filedSep. 27, 2013, which claims the benefit of German Patent Application No.10 2012 109 481.0, filed Oct. 5, 2012 and of U.S. Patent Application No.61/716,845, filed Oct. 22, 2012, the contents of all of which areincorporated by reference herein.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 8,705,016 ('016) describes a laser scanner which, throughuse of a rotatable mirror, emits a light beam into its environment togenerate a three-dimensional (3D) scan. The contents of this patent areincorporated herein by reference.

The subject matter disclosed herein relates to use of a 3D laser scannertime-of-flight (TOF) coordinate measurement device. A 3D laser scannerof this type steers a beam of light to a non-cooperative target such asa diffusely scattering surface of an object. A distance meter in thedevice measures a distance to the object, and angular encoders measurethe angles of rotation of two axles in the device. The measured distanceand two angles enable a processor in the device to determine the 3Dcoordinates of the target.

A TOF laser scanner is a scanner in which the distance to a target pointis determined based on the speed of light in air between the scanner anda target point. Laser scanners are typically used for scanning closed oropen spaces such as interior areas of buildings, industrialinstallations and tunnels. They may be used, for example, in industrialapplications and accident reconstruction applications. A laser scanneroptically scans and measures objects in a volume around the scannerthrough the acquisition of data points representing object surfaceswithin the volume. Such data points are obtained by transmitting a beamof light onto the objects and collecting the reflected or scatteredlight to determine the distance, two-angles (i.e., an azimuth and azenith angle), and optionally a gray-scale value. This raw scan data iscollected, stored and sent to a processor or processors to generate a 3Dimage representing the scanned area or object.

Generating an image requires at least three values for each data point.These three values may include the distance and two angles, or may betransformed values, such as the x, y, z coordinates. In an embodiment,an image is also based on a fourth gray-scale value, which is a valuerelated to irradiance of scattered light returning to the scanner.

Most TOF scanners direct the beam of light within the measurement volumeby steering the light with a beam steering mechanism. The beam steeringmechanism includes a first motor that steers the beam of light about afirst axis by a first angle that is measured by a first angular encoder(or other angle transducer). The beam steering mechanism also includes asecond motor that steers the beam of light about a second axis by asecond angle that is measured by a second angular encoder (or otherangle transducer).

Many contemporary laser scanners include a camera mounted on the laserscanner for gathering camera digital images of the environment and forpresenting the camera digital images to an operator of the laserscanner. By viewing the camera images, the operator of the scanner candetermine the field of view of the measured volume and adjust settingson the laser scanner to measure over a larger or smaller region ofspace. In addition, the camera digital images may be transmitted to aprocessor to add color to the scanner image. To generate a color scannerimage, at least three positional coordinates (such as x, y, z) and threecolor values (such as red, green, blue “RGB”) are collected for eachdata point.

A 3D image of a scene may require multiple scans from differentregistration positions. The overlapping scans are registered in a jointcoordinate system, for example, as described in U.S. Published PatentApplication No. 2012/0069352 ('352), the contents of which areincorporated herein by reference. Such registration is performed bymatching targets in overlapping regions of the multiple scans. Thetargets may be artificial targets such as spheres or checkerboards orthey may be natural features such as corners or edges of walls. Someregistration procedures involve relatively time-consuming manualprocedures such as identifying by a user each target and matching thetargets obtained by the scanner in each of the different registrationpositions. Some registration procedures also require establishing anexternal “control network” of registration targets measured by anexternal device such as a total station. The registration methoddisclosed in '352 eliminates the need for user matching of registrationtargets and establishing of a control network.

However, even with the simplifications provided by the methods of '352,it is today still difficult to remove the need for a user to carry outthe manual registration steps as described above. In a typical case,only 30% of 3D scans can be automatically registered to scans taken fromother registration positions. Today such registration is seldom carriedout at the site of the 3D measurement but instead in an office followingthe scanning procedure. In a typical case, a project requiring a week ofscanning requires two to five days to manually register the multiplescans. This adds to the cost of the scanning project. Furthermore, themanual registration process sometimes reveals that the overlap betweenadjacent scans was insufficient to provide proper registration. In othercases, the manual registration process may reveal that certain sectionsof the scanning environment have been omitted. When such problems occur,the operator must return to the site to obtain additional scans. In somecases, it is not possible to return to a site. A building that wasavailable for scanning at one time may be impossible to access at alater time. A forensics scene of an automobile accident or a homicide isoften not available for taking of scans for more than a short time afterthe incident.

Accordingly, while existing 3D scanners are suitable for their intendedpurposes, what is needed is a 3D scanner having certain features ofembodiments of the present invention.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, a method for measuring andregistering three-dimensional (3D) coordinates comprises: fixedlylocating a measuring device in a first registration position, themeasuring device including a 3D scanner on a moveable platform;obtaining with the 3D scanner, while in the first registration position,3D coordinates of a first collection of points on an object, the 3Dscanner configured to determine the 3D coordinates of the firstcollection of points by projecting a beam of light onto the object andobtaining for each point in the first collection of points a distanceand two angles in response, the distance based at least in part on aspeed of light in air; obtaining by the 3D scanner a first plurality of2D scan sets while the measuring device moves from the firstregistration position to a second registration position, each of thefirst plurality of 2D scan sets being a set of 2D coordinates of pointson the object, each of the first plurality of 2D scan sets beingcollected by the 3D scanner at a different position relative to thefirst registration position; determining for the measuring device afirst translation value corresponding to a first translation direction,a second translation value corresponding to a second translationdirection, and a first rotation value corresponding to a firstorientational axis, wherein the first translation value, the secondtranslation value, and the first rotation value are determined based atleast in part on a fitting of the first plurality of 2D scan setsaccording to a first mathematical criterion; obtaining with the 3Dscanner, while in the second registration position, 3D coordinates of asecond collection of points on the object; determining by the measuringdevice, while the measuring device moves from the second registrationposition to a third registration position, a correspondence amongregistration targets present in both the first collection of points andthe second collection of points, the correspondence based at least inpart on the first translation value, the second translation value, andthe first rotation value; and storing the first translation value, thesecond translation value, and the first rotation value.

These and other advantages and features will become more apparent fromthe following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWING

The subject matter, which is regarded as the invention, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of a laser scanner in accordance with anembodiment of the invention;

FIG. 2 is a side view of the laser scanner illustrating a method ofmeasurement;

FIG. 3 is a schematic illustration of the optical, mechanical, andelectrical components of the laser scanner;

FIG. 4 depicts a planar view of a 3D scanned image;

FIG. 5 depicts an embodiment of a panoramic view of a 3D scanned imagegenerated by mapping a planar view onto a sphere;

FIGS. 6A, 6B and 6C depict a embodiments of a 3D view of a 3D scannedimage;

FIG. 7 depicts an embodiment of a 3D view made up of an image of theobject of FIG. 6B but viewed from a different perspective and shown onlypartially;

FIG. 8A is a perspective view of a 3D measuring device according to anembodiment;

FIG. 8B is a front view of a 3D scanner used to collect 3D coordinatedata while scanning along a horizontal plane according to an embodiment;

FIG. 9 is a block diagram depicting a processor system according to anembodiment;

FIG. 10 is a schematic representation of a 3D scanner measuring anobject from two registration positions according to an embodiment;

FIG. 11 is a schematic representation of a 3D scanner measuring theobject by scanning along a horizontal plane from a plurality ofintermediate positions according to an embodiment;

FIG. 12 shows a 3D scanner capturing portions of the object by scanningalong a horizontal plane from a plurality of positions according to anembodiment;

FIG. 13 shows the 3D scanner capturing portions of the object byscanning along a horizontal plane from a plurality of positions, as seenfrom a frame of reference of the 3D scanner, according to an embodiment;

FIGS. 14A, 14B and 14C illustrate a method for finding changes in theposition and orientation of the 3D scanner over time according to anembodiment;

FIG. 15 includes steps in a method for measuring and registering 3Dcoordinates with a 3D measuring device according to an embodiment;

FIG. 16 is a perspective view of a 3D measuring device that includes a3D scanner, 2D scanner, computing devices, and moveable platformaccording to an embodiment; and

FIG. 17 includes steps in a method for measuring and registering 3Dcoordinates with a 3D measuring device according to an embodiment.

The detailed description explains embodiments of the invention, togetherwith advantages and features, by way of example with reference to thedrawings.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a device that includes a 3D scannerused in two modes, a first mode in which 3D coordinates of an objectsurface are obtained over points over a 3D region of space and a secondmode in which 3D coordinates of an object surface are collected along ahorizontal plane, where the two modes of the 3D scanner are usedtogether to provide automatic registration of 3D scans over a 3D regionof space encompassing more than one scan of 3D regions of space.

Referring now to FIGS. 1-3, a laser scanner 20 is shown for opticallyscanning and measuring the environment surrounding the laser scanner 20.The laser scanner 20 has a measuring head 22 and a base 24. Themeasuring head 22 is mounted on the base 24 such that the laser scanner20 may be rotated about a vertical axis 23. In one embodiment, themeasuring head 22 includes a gimbal point 27 that is a center ofrotation about the vertical axis 23 and a horizontal axis 25. Themeasuring head 22 has a rotary mirror 26, which may be rotated about thehorizontal axis 25. The rotation about the vertical axis may be aboutthe center of the base 24. The terms vertical axis and horizontal axisrefer to the scanner in its normal upright position. It is possible tooperate a 3D coordinate measurement device on its side or upside down,and so to avoid confusion, the terms azimuth axis and zenith axis may besubstituted for the terms vertical axis and horizontal axis,respectively. The term pan axis or standing axis may also be used as analternative to vertical axis.

The measuring head 22 is further provided with an electromagneticradiation emitter, such as light emitter 28, for example, that emits anemitted light beam 30. In one embodiment, the emitted light beam 30 is acoherent light beam such as a laser beam. The laser beam may have awavelength range of approximately 300 to 1600 nanometers, for example790 nanometers, 905 nanometers, 1550 nanometers, or less than 400nanometers. It should be appreciated that other electromagneticradiation beams having greater or smaller wavelengths may also be used.The emitted light beam 30 is amplitude or intensity modulated, forexample, with a sinusoidal waveform or with a rectangular waveform. Theemitted light beam 30 is emitted by the light emitter 28 onto the rotarymirror 26, where it is deflected to the environment. A reflected lightbeam 32 is reflected from the environment by an object 34. The reflectedor scattered light is intercepted by the rotary mirror 26 and directedinto a light receiver 36. The directions of the emitted light beam 30and the reflected light beam 32 result from the angular positions of therotary mirror 26 and the measuring head 22 about the axes 25 and 23,respectively. These angular positions in turn depend on thecorresponding rotary drives or motors.

Coupled to the light emitter 28 and the light receiver 36 is acontroller 38. The controller 38 determines, for a multitude ofmeasuring points X, a corresponding number of distances d between thelaser scanner 20 and the points X on object 34. The distance to aparticular point X is determined based at least in part on the speed oflight in air through which electromagnetic radiation propagates from thedevice to the object point X. In one embodiment the phase shift ofmodulation in light emitted by the laser scanner 20 and the point X isdetermined and evaluated to obtain a measured distance d.

The speed of light in air depends on the properties of the air such asthe air temperature, barometric pressure, relative humidity, andconcentration of carbon dioxide. Such air properties influence the indexof refraction n of the air. The speed of light in air is equal to thespeed of light in vacuum c divided by the index of refraction. In otherwords, c_(air)=c/n. A laser scanner of the type discussed herein isbased on the time-of-flight (TOF) of the light in the air (theround-trip time for the light to travel from the device to the objectand back to the device). Examples of TOF scanners include scanners thatmeasure round trip time using the time interval between emitted andreturning pulses (pulsed TOF scanners), scanners that modulate lightsinusoidally and measure phase shift of the returning light (phase-basedscanners), as well as many other types. A method of measuring distancebased on the time-of-flight of light depends on the speed of light inair and is therefore easily distinguished from methods of measuringdistance based on triangulation. Triangulation-based methods involveprojecting light from a light source along a particular direction andthen intercepting the light on a camera pixel along a particulardirection. By knowing the distance between the camera and the projectorand by matching a projected angle with a received angle, the method oftriangulation enables the distance to the object to be determined basedon one known length and two known angles of a triangle. The method oftriangulation, therefore, does not directly depend on the speed of lightin air.

In one mode of operation, the scanning of the volume around the laserscanner 20 takes place by rotating the rotary mirror 26 relativelyquickly about axis 25 while rotating the measuring head 22 relativelyslowly about axis 23, thereby moving the assembly in a spiral pattern.In an exemplary embodiment, the rotary mirror rotates at a maximum speedof 5820 revolutions per minute. For such a scan, the gimbal point 27defines the origin of the local stationary reference system. The base 24rests in this local stationary reference system.

In addition to measuring a distance d from the gimbal point 27 to anobject point X, the scanner 20 may also collect gray-scale informationrelated to the received optical power (equivalent to the term“brightness.”) The gray-scale value may be determined at least in part,for example, by integration of the bandpass-filtered and amplifiedsignal in the light receiver 36 over a measuring period attributed tothe object point X.

The measuring head 22 may include a display device 40 integrated intothe laser scanner 20. The display device 40 may include a graphicaltouch screen 41, as shown in FIG. 1, which allows the operator to setthe parameters or initiate the operation of the laser scanner 20. Forexample, the screen 41 may have a user interface that allows theoperator to provide measurement instructions to the device, and thescreen may also display measurement results.

The laser scanner 20 includes a carrying structure 42 that provides aframe for the measuring head 22 and a platform for attaching thecomponents of the laser scanner 20. In one embodiment, the carryingstructure 42 is made from a metal such as aluminum. The carryingstructure 42 includes a traverse member 44 having a pair of walls 46, 48on opposing ends. The walls 46, 48 are parallel to each other and extendin a direction opposite the base 24. Shells 50, 52 are coupled to thewalls 46, 48 and cover the components of the laser scanner 20. In theexemplary embodiment, the shells 50, 52 are made from a plasticmaterial, such as polycarbonate or polyethylene for example. The shells50, 52 cooperate with the walls 46, 48 to form a housing for the laserscanner 20.

On an end of the shells 50, 52 opposite the walls 46, 48 a pair of yokes54, 56 are arranged to partially cover the respective shells 50, 52. Inthe exemplary embodiment, the yokes 54, 56 are made from a suitablydurable material, such as aluminum for example, that assists inprotecting the shells 50, 52 during transport and operation. The yokes54, 56 each includes a first arm portion 58 that is coupled, such aswith a fastener for example, to the traverse 44 adjacent the base 24.The arm portion 58 for each yoke 54, 56 extends from the traverse 44obliquely to an outer corner of the respective shell 50, 52. From theouter corner of the shell, the yokes 54, 56 extend along the side edgeof the shell to an opposite outer corner of the shell. Each yoke 54, 56further includes a second arm portion that extends obliquely to thewalls 46, 48. It should be appreciated that the yokes 54, 56 may becoupled to the traverse 42, the walls 46, 48 and the shells 50, 52 atmultiple locations.

The pair of yokes 54, 56 cooperate to circumscribe a convex space withinwhich the two shells 50, 52 are arranged. In the exemplary embodiment,the yokes 54, 56 cooperate to cover all of the outer edges of the shells50, 54, while the top and bottom arm portions project over at least aportion of the top and bottom edges of the shells 50, 52. This providesadvantages in protecting the shells 50, 52 and the measuring head 22from damage during transportation and operation. In other embodiments,the yokes 54, 56 may include additional features, such as handles tofacilitate the carrying of the laser scanner 20 or attachment points foraccessories for example.

On top of the traverse 44, a prism 60 is provided. The prism extendsparallel to the walls 46, 48. In the exemplary embodiment, the prism 60is integrally formed as part of the carrying structure 42. In otherembodiments, the prism 60 is a separate component that is coupled to thetraverse 44. When the mirror 26 rotates, during each rotation the mirror26 directs the emitted light beam 30 onto the traverse 44 and the prism60. Due to non-linearities in the electronic components, for example inthe light receiver 36, the measured distances d may depend on signalstrength, which may be measured in optical power entering the scanner oroptical power entering optical detectors within the light receiver 36,for example. In an embodiment, a distance correction is stored in thescanner as a function (possibly a nonlinear function) of distance to ameasured point and optical power (generally unscaled quantity of lightpower sometimes referred to as “brightness”) returned from the measuredpoint and sent to an optical detector in the light receiver 36. Sincethe prism 60 is at a known distance from the gimbal point 27, themeasured optical power level of light reflected by the prism 60 may beused to correct distance measurements for other measured points, therebyallowing for compensation to correct for the effects of environmentalvariables such as temperature. In the exemplary embodiment, theresulting correction of distance is performed by the controller 38.

In an embodiment, the base 24 is coupled to a swivel assembly (notshown) such as that described in commonly owned U.S. Pat. No. 8,705,012('012), which is incorporated by reference herein. The swivel assemblyis housed within the carrying structure 42 and includes a motor that isconfigured to rotate the measuring head 22 about the axis 23.

An auxiliary image acquisition device 66 may be a device that capturesand measures a parameter associated with the scanned volume or thescanned object and provides a signal representing the measuredquantities over an image acquisition area. The auxiliary imageacquisition device 66 may be, but is not limited to, a pyrometer, athermal imager, an ionizing radiation detector, or a millimeter-wavedetector. In an embodiment, the auxiliary image acquisition device 66 isa color camera.

In an embodiment, a central color camera (first image acquisitiondevice) 112 is located internally to the scanner and may have the sameoptical axis as the 3D scanner device. In this embodiment, the firstimage acquisition device 112 is integrated into the measuring head 22and arranged to acquire images along the same optical pathway as emittedlight beam 30 and reflected light beam 32. In this embodiment, the lightfrom the light emitter 28 reflects off a fixed mirror 116 and travels todichroic beam-splitter 118 that reflects the light 117 from the lightemitter 28 onto the rotary mirror 26. The dichroic beam-splitter 118allows light to pass through at wavelengths different than thewavelength of light 117. For example, the light emitter 28 may be a nearinfrared laser light (for example, light at wavelengths of 780 nm or1150 nm), with the dichroic beam-splitter 118 configured to reflect theinfrared laser light while allowing visible light (e.g., wavelengths of400 to 700 nm) to transmit through. In other embodiments, thedetermination of whether the light passes through the beam-splitter 118or is reflected depends on the polarization of the light. The digitalcamera 112 takes 2D photographic images of the scanned area to capturecolor data to add to the scanned image. In the case of a built-in colorcamera having an optical axis coincident with that of the 3D scanningdevice, the direction of the camera view may be easily obtained bysimply adjusting the steering mechanisms of the scanner—for example, byadjusting the azimuth angle about the axis 23 and by steering the mirror26 about the axis 25.

FIG. 4 depicts an example of a planar view of a 3D scanned image 400.The planar view depicted in FIG. 4 maps an image based on direct mappingof data collected by the scanner. The scanner collects data in aspherical pattern but with data points collected near the poles moretightly compressed than those collected nearer the horizon. In otherwords, each point collected near a pole represents a smaller solid anglethan does each point collected nearer the horizon. Since data from thescanner may be directly represented in rows and column, data in a planarimage is conveniently presented in a rectilinear format, as shown inFIG. 4. With planar mapping described above, straight lines appear to becurved, as for example the straight fence railings 420 that appearcurved in the planar view of the 3D image. The planar view may be a 3Dunprocessed scanned image displaying just the gray-scale values receivedfrom the distance sensor arranged in columns and rows as they wererecorded. In addition, the 3D unprocessed scanned image of the planarview may be in full resolution or reduced resolution depending on systemcharacteristics (e.g., display device, storage, processor). The planarview may be a 3D processed scanned image that depicts either gray-scalevalues (resulting from the light irradiance measured by the distancesensor for each pixel) or color values (resulting from camera imageswhich have been mapped onto the scan). Although the planar viewextracted from the 3D scanner is ordinarily a gray-scale or color image,FIG. 4 is shown as a line drawing for clarity in document reproduction.The user interface associated with the display unit, which may beintegral to the laser scanner, may provide a point selection mechanism,which in FIG. 4 is the cursor 410. The point selection mechanism may beused to reveal dimensional information about the volume of space beingmeasured by the laser scanner. In FIG. 4, the row and column at thelocation of the cursor are indicated on the display at 430. The twomeasured angles and one measured distance (the 3D coordinates in aspherical coordinate system) at the cursor location are indicated on thedisplay at 440. Cartesian XYZ coordinate representations of the cursorlocation are indicated on the display at 450.

FIG. 5 depicts an example of a panoramic view of a 3D scanned image 600generated by mapping a planar view onto a sphere, or in some cases acylinder. A panoramic view can be a 3D processed scanned image (such asthat shown in FIG. 5) in which 3D information (e.g., 3D coordinates) isavailable. The panoramic view may be in full resolution or reducedresolution depending on system characteristics. It should be pointed outthat an image such as FIG. 5 is a 2D image that represents a 3D scenewhen viewed from a particular perspective. In this sense, the image ofFIG. 5 is much like an image that might be captured by a 2D camera or ahuman eye. Although the panoramic view extracted from the 3D scanner isordinarily a gray-scale or color image, FIG. 5 is shown as a linedrawing for clarity in document reproduction.

The term panoramic view refers to a display in which angular movement isgenerally possible about a point in space, but translational movement isnot possible (for a single panoramic image). In contrast, the term 3Dview as used herein refers to generally refers to a display in whichprovision is made (through user controls) to enable not only rotationabout a fixed point but also translational movement from point to pointin space.

FIGS. 6A, 6B and 6C depict an example of a 3D view of a 3D scannedimage. In the 3D view a user can leave the origin of the scan and seethe scan points from different viewpoints and angles. The 3D view is anexample of a 3D processed scanned image. The 3D view may be in fullresolution or reduced resolution depending on system characteristics. Inaddition, the 3D view allows multiple registered scans to be displayedin one view. FIG. 6A is a 3D view 710 over which a selection mask 730has been placed by a user. FIG. 6B is a 3D view 740 in which only thatpart of the 3D view 710 covered by the selection mask 730 has beenretained. FIG. 6C shows the same 3D measurement data as in FIG. 6Bexcept as rotated to obtain a different view. FIG. 7 shows a differentview of FIG. 6B, the view in this instance being obtained from atranslation and rotation of the observer viewpoint, as well as areduction in observed area. Although the 3D views extracted from the 3Dscanner is ordinarily a gray-scale or color image, FIGS. 6A-C and 7 areshown as line drawings for clarity in document reproduction.

FIGS. 8A, 8B and 9 show an embodiment of a 3D measuring device 800 thatincludes a 3D scanner 20, a processor system 950, and an optionalmoveable platform 820. The 3D measuring device 800 may be a 3D TOFscanner 20 as described in reference to FIG. 1.

The processor system 950 includes one or more processing elements thatmay include a 3D scanner processor (controller) 38, an external computer970, and a cloud computer 980. The processors may be microprocessors,field programmable gate arrays (FPGAs), digital signal processors(DSPs), and generally any device capable of performing computingfunctions. The one or more processors have access to memory for storinginformation. In an embodiment illustrated in FIG. 9, the controller 38represents one or more processors distributed throughout the 3D scanner.Also included in the embodiment of FIG. 9 are an external computer 970and one or more cloud computers 980 for remote computing capability. Inan alternative embodiment, only one or two of the processors 38, 970,and 980 is provided in the processor system. Communication among theprocessors may through wired links, wireless links, or a combination ofwired and wireless links. In an embodiment, scan results are uploadedafter each scanning session to the cloud (remote network) for storageand future use.

In one mode of operation the 3D scanner 20 measures 2D coordinates in ahorizontal plane. In most cases, it does this by steering light within ahorizontal plane to illuminate object points in the environment. Itcollects the reflected (scattered) light from the objects points todetermine 2D coordinates of the object points in the horizontal plane.In an embodiment, the 3D scanner scans a spot of light measures theangle of rotation about the axis 23 with an angular encoder while at thesame time measuring a corresponding distance value to each illuminatedobject point in the horizontal plane. The 3D scanner 23 may rotate aboutthe axis 23 at a relatively high speed while performing no rotationabout the axis 25. In an embodiment, the laser power is set to fallwithin eye safety limits.

An optional position/orientation sensor 920 in the 3D scanner 20 mayinclude inclinometers (accelerometers), gyroscopes, magnetometers, andaltimeters. Usually devices that include one or more of an inclinometerand gyroscope are referred to as an inertial measurement unit (IMU). Insome cases, the term IMU is used in a broader sense to include a varietyof additional devices that indicate position and/or orientation—forexample, magnetometers that indicate heading based on changes inmagnetic field direction relative to the earth's magnetic north andaltimeters that indicate altitude (height). An example of a widely usedaltimeter is a pressure sensor. By combining readings from a combinationof position/orientation sensors with a fusion algorithm that may includea Kalman filter, relatively accurate position and orientationmeasurements can be obtained using relatively low-cost sensor devices.

The optional moveable platform 820 enables the 3D measuring device 20 tobe moved from place to place, typically along a floor that isapproximately horizontal. In an embodiment, the optional moveableplatform 820 is a tripod that includes wheels 822. In an embodiment, thewheels 822 may be locked in place using wheel brakes 824. In anotherembodiment, the wheels 822 are retractable, enabling the tripod to sitstably on three feet attached to the tripod. In another embodiment, thetripod has no wheels but is simply pushed or pulled along a surface thatis approximately horizontal, for example, a floor. In anotherembodiment, the optional moveable platform 820 is a wheeled cart thatmay be hand pushed/pulled or motorized.

In an embodiment, in one mode of operation, the 3D scanner 20 isconfigured to scan a beam of light over a range of angles in ahorizontal plane. At instants in time the 3D scanner 20 returns an anglereading and a corresponding distance reading to provide 2D coordinatesof object points in the horizontal plane. In completing one scan overthe full range of angles, the 3D scanner 20 returns a collection ofpaired angle and distance readings. As the 3D measuring device 800 ismoved from place to place, it continues to return 2D coordinate valuesin a horizontal plane. These 2D coordinate values are used to locate theposition of the 3D scanner 20 at each stationary registration position,thereby enabling more accurate registration.

FIG. 10 shows the 3D measuring device 800 moved to a first registrationposition 1112 in front of an object 1102 that is to be measured. Theobject 1102 might for example be a wall in a room. In an embodiment, the3D measuring device 800 is brought to a stop and is held in place withbrakes, which in an embodiment are brakes 824 on wheels 822. The 3Dscanner 20 in the 3D measuring device 800 takes a first 3D scan of theobject 1102. In an embodiment, the 3D scanner 20 may if desired obtain3D measurements in all directions except in downward directions blockedby the structure of the 3D measuring device 800. However, in the exampleof FIG. 10, in which 3D scanner 20 measures a long, mostly flatstructure 1102, a smaller effective FOV 1130 may be selected to providea more face-on view of features on the structure.

When the first 3D scan is completed, the processor system 950 causes the3D scanner 20 to change from 3D scanning mode to 2D scanning mode. In anembodiment, it does this by fixing the mirror 26 to direct the outgoingbeam 30 on a horizontal plane. The mirror receives reflected light 32traveling in the reverse direction. In an embodiment, the scanner beginsthe 2D scan as soon as the 3D scanning stops. In another embodiment, the2D scan starts when the processor receives a signal such as a signalform the position/orientation sensor 920, a signal from a brake releasesensor, or a signal sent in response to a command from an operator. The3D scanner 20 may start to collect 2D scan data when the 3D measuringdevice 800 starts to move. In an embodiment, the 2D scan data is sent tothe processor system 950 as it is collected.

In an embodiment, the 2D scan data is collected as the 3D measuringdevice 800 is moved toward the second registration position 1114. In anembodiment, 2D scan data is collected and processed as the 3D scanner 20passes through a plurality of 2D measuring positions 1120. At eachmeasuring position 1120, the 3D scanner collects 2D coordinate data overan effective FOV 1140. Using methods described in more detail below, theprocessor system 950 uses 2D scan data from the plurality of 2D scans atpositions 1120 to determine a position and orientation of the 3D scanner20 at the second registration position 1114 relative to the firstregistration position 1112, where the first registration position andthe second registration position are known in a 3D coordinate systemcommon to both. In an embodiment, the common coordinate system isrepresented by 2D Cartesian coordinates x, y and by an angle of rotationθ relative to the x or y axis. In an embodiment, the x and y axes lie inthe horizontal x-y plane of the 3D scanner 20 and may be further basedon a direction of a “front” of the 3D scanner 20. An example of such an(x, y, θ) coordinate system is the coordinate system 1410 of FIG. 14A.

On the object 1102, there is a region of overlap 1150 between the first3D scan (collected at the first registration position 1112) and thesecond 3D scan (collected at the second registration position 1114). Inthe overlap region 1150 there are registration targets (which may benatural features of the object 1102) that are seen in both the first 3Dscan and the second 3D scan. A problem that often occurs in practice isthat, in moving the 3D scanner 20 from the first registration position1112 to the second registration position 1114, the processor system 950loses track of the position and orientation of the 3D scanner 20 andhence is unable to correctly associate the registration targets in theoverlap regions to enable the registration procedure to be performedreliably. By using the succession of 2D scans, the processor system 950is able to determine the position and orientation of the 3D scanner 20at the second registration position 1114 relative to the firstregistration position 1112. This information enables the processorsystem 950 to correctly match registration targets in the region ofoverlap 1150, thereby enabling the registration procedure to be properlycompleted.

FIG. 12 shows the 3D scanner 20 collecting 2D scan data at selectedpositions 1120 over an effective FOV 1140. At different positions 1120,the 3D scanner captures 2D scan data over a portion of the object 1102marked A, B, C, D, and E. FIG. 12 shows the 3D scanner 20 moving in timerelative to a fixed frame of reference of the object 1102.

FIG. 13 includes the same information as FIG. 12 but shows it from theframe of reference of the 3D scanner 20 while taking 2D scans ratherthan the frame of reference of the object 1102. This figure makes clearthat in the scanner frame of reference, the position of features on theobject change over time. Hence it is clear that the distance traveled bythe 3D scanner 20 between registration position 1 and registrationposition 2 can be determined from the 2D scan data sent from the 3Dscanner 20 to the processor system 950.

FIG. 14A shows a coordinate system that may be used in FIGS. 14B and14C. In an embodiment, the 2D coordinates x and y are selected to lie onthe plane in which the 2D scans are taken, ordinarily the horizontalplane. The angle θ is selected as a rotation angle in the plane, therotation angle relative to an axis such as x or y. FIGS. 14B, 14Crepresent a realistic case in which the 3D scanner 20 is moved notexactly on a straight line, say nominally parallel to the object 1102,but also to the side. Furthermore, the 3D scanner 20 may be rotated asit is moved.

FIG. 14B shows the movement of the object 1102 as seen from the frame ofreference of the 3D scanner 20 in traveling from the first registrationposition to the second registration position. In the scanner frame ofreference (that is, as seen from the scanner's point of view), theobject 1102 is moving while the 3D scanner 20 is fixed in place. In thisframe of reference, the portions of the object 1102 seen by the 3Dscanner 20 appear to translate and rotate in time. The 3D scanner 20provides a succession of such translated and rotated 2D scans to theprocessor system 950. In the example shown in FIGS. 14A, B, the scannertranslates in the +y direction by a distance 1420 shown in FIG. 14B androtates by an angle 1430, which in this example is +5 degrees. Ofcourse, the scanner could equally well have moved in the +x or −xdirection by a small amount. To determine the movement of the 3D scanner20 in the x, y, θ directions, the processor system 950 uses the datarecorded in successive horizontal scans as seen in the frame ofreference of the scanner 20, as shown in FIG. 14B. In an embodiment, theprocessor system 950 performs a best-fit calculation using methods wellknown in the art to match the two scans or features in the two scans asclosely as possible.

As the 3D scanner 20 takes successive 2D readings and performs best-fitcalculations, the processor system 950 keeps track of the translationand rotation of the 3D scanner 20. In this way, the processor system 950is able to accurately determine the change in the values of x, y, θ asthe measuring device 800 moves from the first registration position 1112to the second registration position 1114.

It is important to understand that the processor system 950 determinesthe position and orientation of the 3D measuring device 800 based on acomparison of the succession of 2D scans and not on fusion of the 2Dscan data with 3D scan data provided by the 3D scanner 20 at the firstregistration position 1112 or the second registration position 1114.

Instead, the processor system 950 is configured to determine a firsttranslation value, a second translation value, and a first rotationvalue that, when applied to a combination of the first 2D scan data andsecond 2D scan data, results in transformed first 2D data that matchestransformed second 2D data as closely as possible according to anobjective mathematical criterion. In general, the translation androtation may be applied to the first scan data, the second scan data, orto a combination of the two. For example, a translation applied to thefirst data set is equivalent to a negative of the translation applied tothe second data set in the sense that both actions produce the samematch in the transformed data sets. An example of an “objectivemathematical criterion” is that of minimizing the sum of squaredresidual errors for those portions of the scan data judged to overlap.Another type of objective mathematical criterion may involve a matchingof multiple features identified on the object. For example, suchfeatures might be the edge transitions 1103, 1104, and 1105 shown inFIG. 11B. The mathematical criterion may involve processing of the raw2D scan data provided by the 3D scanner 20 to the processor system 950,or it may involve a first intermediate level of processing in whichfeatures are represented as a collection of line segments using methodsthat are known in the art, for example, methods based on the IterativeClosest Point (ICP). Such a method based on ICP is described in Censi,A., “An ICP variant using a point-to-line metric,” IEEE InternationalConference on Robotics and Automation (ICRA) 2008.

In an embodiment, the first translation value is dx, the secondtranslation value is dy, and the first rotation value dθ. If first 2Dscan data has translational and rotational coordinates (in a referencecoordinate system) of (x₁, y₁, θ₁), then the second 2D scan datacollected at a second location has coordinates given by (x₂, y₂,θ₂)=(x₁+dx, y₁+dy, θ₁+dθ). It an embodiment, the processor system 950 isfurther configured to determine a third translation value (for example,dz) and a second and third rotation values (for example, pitch androll). The third translation value, second rotation value, and thirdrotation value may be determined based at least in part on readings fromthe position/orientation sensor 920.

The 3D scanner 20 collects 2D scan data at the first registrationposition 1112 and more 2D scan data at the second registration position1114. In some cases, these 2D scans may suffice to determine theposition and orientation of the 3D measuring device at the secondregistration position 1114 relative to the first registration position1112. In other cases, the two sets of 2D scan data are not sufficient toenable the processor system 950 to accurately determine the firsttranslation value, the second translation value, and the first rotationvalue. This problem may be avoided by collecting 2D scan data atintermediate scan locations 1120. In an embodiment, the 2D scan data iscollected and processed at regular intervals, for example, once persecond. In this way, features are easily identified in successive 2Dscans 1120. If more than two 2D scans are obtained, the processor system950 may choose to use the information from all the successive 2D scansin determining the translation and rotation values in moving from thefirst registration position 1112 to the second registration position1114. Alternatively, the processor may choose to use only the first andlast scans in the final calculation, simply using the intermediate 2Dscans to ensure proper correspondence of matching features. In mostcases, accuracy of matching is improved by incorporating informationfrom multiple successive 2D scans.

The 3D measuring device 800 is moved to the second registration position1114. In an embodiment, the 3D measuring device 800 is brought to a stopand brakes are locked to hold the 3D scanner stationary. In analternative embodiment, the processor system 950 starts the 3D scanautomatically when the moveable platform is brought to a stop, forexample, by the position/orientation sensor 920 noting the lack ofmovement. The 3D scanner 20 in the 3D measuring device 800 takes a 3Dscan of the object 1102. This 3D scan is referred to as the second 3Dscan to distinguish it from the first 3D scan taken at the firstregistration position.

The processor system 950 applies the already calculated firsttranslation value, the second translation value, and the first rotationvalue to adjust the position and orientation of the second 3D scanrelative to the first 3D scan. This adjustment, which may be consideredto provide a “first alignment,” brings the registration targets (whichmay be natural features in the overlap region 1150) into closeproximity. The processor system 950 performs a fine registration inwhich it makes fine adjustments to the six degrees of freedom of thesecond 3D scan relative to the first 3D scan. It makes the fineadjustment based on an objective mathematical criterion, which may bethe same as or different than the mathematical criterion applied to the2D scan data. For example, the objective mathematical criterion may bethat of minimizing the sum of squared residual errors for those portionsof the scan data judged to overlap. Alternatively, the objectivemathematical criterion may be applied to a plurality of features in theoverlap region. The mathematical calculations in the registration may beapplied to raw 3D scan data or to geometrical representations of the 3Dscan data, for example, by a collection of line segments.

Outside the overlap region 1150, the aligned values of the first 3D scanand the second 3D scan are combined in a registered 3D data set. Insidethe overlap region, the 3D scan values included in the registered 3Ddata set are based on some combination of 3D scanner data from thealigned values of the first 3D scan and the second 3D scan.

FIG. 15 shows elements of a method 1500 for measuring and registering 3Dcoordinates.

An element 1505 includes providing a 3D measuring device that includes aprocessor system, a 3D scanner, and a moveable platform. The processorsystem has at least one of a 3D scanner controller, an externalcomputer, and a cloud computer configured for remote network access. Anyof these processing elements within the processor system may include asingle processor or multiple distributed processing elements, theprocessing elements being a microprocessor, digital signal processor,FPGA, or any other type of computing device. The processing elementshave access to computer memory. The 3D scanner has a first light source,a first beam steering unit, a first angle measuring device, a secondangle measuring device, and a first light receiver. The first lightsource is configured to emit a first beam of light, which in anembodiment is a beam of laser light. The first beam steering unit isprovided to steer the first beam of light to a first direction onto afirst object point. The beam steering unit may be a rotating mirror suchas the mirror 26 or it may be another type of beam steering mechanism.For example, the 3D scanner may contain a base onto which is placed afirst structure that rotates about a vertical axis, and onto thisstructure may be placed a second structure that rotates about ahorizontal axis. With this type of mechanical assembly, the beam oflight may be emitted directly from the second structure and point in adesired direction. Many other types of beam steering mechanisms arepossible. In most cases, a beam steering mechanism includes one or twomotors. The first direction is determined by a first angle of rotationabout a first axis and a second angle of rotation about a second axis.The first angle measuring device is configured to measure the firstangle of rotation and the second angle measuring device configured tomeasure the second angle of rotation. The first light receiver isconfigured to receive first reflected light, the first reflected lightbeing a portion of the first beam of light reflected by the first objectpoint. The first light receiver is further configured to produce a firstelectrical signal in response to the first reflected light. The firstlight receiver is further configured to cooperate with the processorsystem to determine a first distance to the first object point based atleast in part on the first electrical signal, and the 3D scanner isconfigured to cooperate with the processor system to determine 3Dcoordinates of the first object point based at least in part on thefirst distance, the first angle of rotation and the second angle ofrotation. The moveable platform is configured to carry the 3D scanner.

An element 1510 includes determining with processor system, incooperation with the 3D scanner, 3D coordinates of a first collection ofpoints on an object surface while the 3D scanner is fixedly located at afirst registration position.

An element 1515 includes obtaining by the 3D scanner in cooperation withthe processor system a plurality of 2D scan sets. Each of the pluralityof 2D scan sets is a set of 2D coordinates of points on the objectsurface collected as the 3D scanner moves from the first registrationposition to a second registration position. Each of the plurality of 2Dscan sets is collected by the 3D scanner at a different positionrelative to the first registration position. In an embodiment, each 2Dscan set lies in a horizontal plane.

An element 1520 includes determining by the processor system a firsttranslation value corresponding to a first translation direction, asecond translation value corresponding to a second translationdirection, and a first rotation value corresponding to a firstorientational axis, wherein the first translation value, the secondtranslation value, and the first rotation value are determined based atleast in part on a fitting of the plurality of 2D scan sets according toa first mathematical criterion. In an embodiment, the first orientationaxis is a vertical axis perpendicular to the planes in which the 2D scansets are collected.

An element 1525 includes determining with the processor system, incooperation with the 3D scanner, 3D coordinates of a second collectionof points on the object surface while the 3D scanner is fixedly locatedat the second registration position.

An element 1535 includes identifying by the processor system acorrespondence among registration targets present in both the firstcollection of points and the second collection of points, thecorrespondence based at least in part on the first translation value,the second translation value, and the first rotation value;

An element 1545 includes determining 3D coordinates of a registered 3Dcollection of points based at least in part on a second mathematicalcriterion, the correspondence among registration targets, the 3Dcoordinates of the first collection of points, and the 3D coordinates ofthe second collection of points. An element 1550 includes storing the 3Dcoordinates of the registered 3D collection of points.

In most methods used today for scanning large objects (for example,large buildings), data is collected at each registration position andthe quality of the registration evaluated later. One problem with thisapproach is that it provides no way to detect a failure in registration,which might be easily corrected on site, but is difficult to correct ata later time when access to the scan site may no longer be available. Inaddition, there is the need with this method to register the multiplescans in software run on an external computer. In some cases, natural orartificial targets observed by the scanner at consecutive registrationlocations may be automatically recognized and matched by the software,but in many cases the scans must be hand registered. In many cases, thetime and effort in registering and processing 3D scan data greatlyoutweighs the time required to collect the scan data on site.

In an embodiment described herein, processing of 2D and 3D scanner datais performed as the measurement is taking place, thereby eliminatingtime-consuming post processing and further ensuring that required scandata has been collected before leaving a site.

An example of a measuring device 800 that may be used to perform thismeasurement was described herein above with reference to FIG. 8. Anotherexample of a measuring device 1600 that may be used to perform thismeasurement is now described with reference to FIG. 16. Included in the3D measuring device 1600 is a 3D TOF scanner 20 that measures distancebased at least in part on a speed of light in air. This type of scanneralso measures two angles using angle transducers such as angularencoders. The two measured angles and one measured distance provide 3Dcoordinates of points on an object. In an embodiment, the scannerincludes motors and a servo system to drive a beam of light to anydesired point on an object. In an embodiment described herein above withrespect to FIGS. 1-3, the scanner may also include a mode for rapidlydirecting the beam of light over a continually varying pattern, therebyenabling rapid collection of 3D coordinates over a large volume.

The 3D measuring device 20 is further configured to emit a beam of lightin a plane 1622, which might be a horizontal plane. In an embodiment,the beam of light sweeps over an angle of 360 degrees at a rate of 10Hz. In an embodiment, the 3D scanner 20 emits a beam of light on anobject, receives reflected light from the object, and determines acollection of distances to the object based on the reflected light. Inan embodiment, in its planar-emission mode, the 3D scanner 1610 measuresdistances as a function of swept angle. In an embodiment, the 3Dmeasuring device further includes an assembly 1620 having a computingdevice 1630 that receives from the 3D scanner 20 the 2D scan sets andthe 3D coordinate data. In an embodiment, the computing device 1630further performs processing of 2D and 3D scan data to determine acorrespondence among targets measured at the first registration positionand the second registration position. In other embodiments, othercomputing devices, such as a computer 1640 or an external computer 1650not attached to the 3D measuring device may be used to determine thecorrespondence among targets measured at the first and secondregistration positions. In another embodiment, all processing of 3D and2D data are carried out by an internal processor within the 3D measuringdevice 20.

Communication channels to transfer information among the 2D scanner, 3Dscanner, and computing devices may be wireless or wired communicationchannels 1660. In an embodiment, a wireless access point (AP) iscontained within the 3D scanner 20. In an embodiment the AP connects towireless devices such as the 2D scanner 1610 and one or more ofcomputing devices 1630, 1640, and 1650. In an alternative embodiment,the 3D scanner 20 includes an automation adapter having an Ethernetinterface and a switch. The automation adapter connects with Ethernetcables of the 2D scanner 1610 and computing devices such as 1630, 1640,and 1650. The automation interface enables wired communication among theelements of the measuring device 1600 and external computing devices. Inan embodiment, the 3D scanner 20 includes both an AP and an automationadapter to provide both wireless and wired communication among differentcomponents of the system. In other embodiments, the AP and automationadapter are not included in the 3D scanner 20 but elsewhere in thesystem.

The measuring device further includes a moveable platform 1605, whichmay be pushed by an operator or moved under computer control bymotorized wheels. The 3D scanner is mounted on the moveable platform1605.

In an embodiment, a first 3D scan is taken at a first registrationposition. The scanner moves between the first registration position andthe second registration position, either under its own power usingmotorized wheels or being pushed by an operator. As it moves between thefirst and second registration position, the 3D scanner obtains 2D scandata, which is then evaluated mathematically to determine a movementvector (distance in each of two directions) and an angle of rotation, asexplained herein above. At the second registration position, the 3Dscanner 20 takes a second 3D scan. As explained herein above, one of thecomputing devices (i.e., processors) uses the plurality of collected 2Dscan sets to determine a correspondence among registration targets seenby the 3D scanner in the first registration position and the secondregistration position. At a later time, a computing device performs anyother steps needed to complete combining and processing of the 3D datacollected at the first and second registration positions. This processof combining may further include additional collected data such as colordata obtained from an internal color camera within the scanner.

The measuring device 1600 moves to successive registration positions,taking a 3D measurement at each registration position and collecting 2Ddata by emitting light in a planar mode between the registrationpositions. An aspect of the present invention is that processing iscarried out between the second and third registration positions todetermine the correspondence between the registration targets observedat the first and second registration positions. This processing uses the2D data collected between the first and second registration positions incombination with 3D data obtained at the first and second registrationpositions.

Hence, when the scanner reaches the third registration position, thecomputing device will have determined (at least partially if notcompletely) the correspondence among the targets in the first and secondregistration positions. If a correspondence was not successfullyestablished by the computing device, a notice may be given indicatingthat the problem is present. This may result in an operator beingnotified or it may result in the measurement suspended. In anembodiment, the failure to register the targets observed by the 3Dscanner at the first and second registration positions results in thescanner being returned to an earlier step to repeat measurements.

In an embodiment, when the computing device has determined thecorrespondence among the targets in the overlap region of the first andsecond registration positions, the measuring device further determines aquality of the correspondence. In an embodiment, the measuring deviceprovides a notification when the quality of the correspondence is belowa quality threshold. The notification may be a notification to the user,a computer message, an emitted sound, an emitted light, or a stopping ofthe inspection procedure, for example.

In an embodiment, the scanner may determine the distance to move themeasuring device 1600 between the first registration position and thesecond registration position based at least in part on one of the 2Dscan sets. In an embodiment, each of the 2D scan sets includesinformation about features observable in a horizontal 2D scan. Examplesof such features are the features 1102-1105 in FIG. 11. In anembodiment, the decision on the distance to be moved between the firstregistration position and the second registration position is basedentirely on the first 2D scan set collected between the first and secondregistration positions. In another embodiment, the decision on thedistance to be moved is based on a plurality of the first 2D scan sets,with the decision on the distance to be moved made during the movementbetween the first and second registration positions.

In an embodiment, the computing device 1640 is a laptop or notebookcomputer that provides a user an interface to a computer programenabling advanced processing and viewing of scan data. In an embodiment,use of the computing device 1640 is optional and simply is provided togive the operator more analysis tools. In another embodiment, thecomputing device 1640 is used to perform correspondence calculationsdescribed herein above or to perform other 3D processing steps.

In an embodiment, a computing device 1630 continually computes theposition of the measuring device 1600 based at least in part on datafrom the 2D scanner and, optionally, on data provided by aposition/orientation sensor, which might include a multi-axisinclinometer, a multi-axis gyroscope, and a magnetometer (electroniccompass) to provide heading information. In an embodiment, data from the2D scanner is acquired at a rate of 10 Hz. In an embodiment, after eachscan, a difference is calculated with respect to one or more 2D scansobtained previously. In an embodiment, this information is provided to aKalman filter that performs “intelligent averaging” calculations thatsmooth out noise within constraints imposed by movement geometry.

In an embodiment, application software runs on a notebook computer 1640or similar device. In an embodiment, the user selects a button on theuser interface of the application software to begin processing of thecollected data. In an embodiment, after collecting after collecting 3Dscan data at the second registration position, the software requests 2Dposition information from processed 2D scan data, which might beprovided for example from the computing device 1630. The processed 2Dscan data may be provided as metadata to the 3D scan. The software usesa registration algorithm to determine a correspondence among theregistration targets in the overlap region between the first and secondregistration positions. The software completes the 3D registration bycombining 3D coordinates obtained at the first and second registrationpositions.

In other embodiments, the calculations are performed without the userneeding to press a button on the user interface of an applicationprogram running on a notebook computer 1640. In an embodiment,measurements are carried out in an integrated and automatic way withoutrequiring assistance of an operator. In an embodiment, additionalcalculations, which may involve including additional mathematicaloperations such as meshing registered 3D data, and adding and texture toregistered 3D data may be carried out following the registration step.In an embodiment, these later processing steps may be carried out inparallel, for example, by network computers to provide finished 3D scansat the end of data collection by the measuring device 1600.

FIG. 17 is a flow chart of a method 1700 that may be carried outaccording to the description given herein above. In the element 1705,the measuring device 1600 is fixedly located in a first registrationposition such as the position 1112 in FIG. 10. The measuring deviceincludes a 3D scanner 20 configured to operate in both a 3D scanningmode and a 2D planer-scanner mode. The 3D scanner 20 is mounted on amoveable platform 1605, which in FIG. 16 is a tripod mounted on aplatform having three wheels. In an embodiment, in its planar-scanningmode, the 3D scanner emits a beam of light that sweeps in differentdirections in a horizontal plane 1622.

In the element 1710, the 3D scanner, while in the first registrationposition, obtains 3D coordinates of a first collection of points on anobject, which in an embodiment illustrated in FIGS. 10 and 11 is theside of a building. In an embodiment, the 3D scanner is a TOF scanner,which may be of a variety of types. An example of a possible TOF scanneris the scanner 20 discussed in reference to FIGS. 1-3.

In the element 1715, the 3D scanner operates in its planer-scanning modeto obtain a first plurality of 2D scan sets while the first measuringdevice moves from the first registration position to the secondregistration position. Each of the first plurality of 2D scan setsincludes a set of 2D coordinates of points on the object. The 2Dcoordinates of points on the object may be given in any coordinatesystem, for example, as x-y values or as distance and angle values. Eachof the first plurality of 2D scan sets is collected by the 3D scanner ata different position relative to the first registration position.

In the element 1720, the measuring device determines a first translationvalue corresponding to a first translation direction, a secondtranslation value corresponding to a second translation direction, and afirst rotation value corresponding to a first orientational axis. Thefirst translational direction and the second translational directionmight be, for example, x-y coordinates in a coordinate systemestablished with respect to the object being measured. For example, thex-y coordinates might correspond to coordinates along a floor on whichthe measuring device moves. Other coordinate systems may alternativelybe used to represent the first translational direction and the secondtranslational direction. The first orientational axis has a givendirection in relation to the first and second translation directions. Aconvenient choice for the first orientational axis is a directionperpendicular to the plane containing vectors along the first and secondtranslational directions. The first translation value, the secondtranslation value, and the first rotation angle provide the informationneeded to obtain a good initial estimate of the pose of the scanner atthe second registration position relative to the pose of the scanner atthe first registration position. This provides a good basis for matchingthe registration targets, whether natural targets or artificial targets,seen from the first and second registration positions. The determiningof the first translation value, the second translation value, and thefirst rotation angle is carried out according to a first mathematicalcriterion. Such a mathematical criterion is also referred to as anobjective mathematical criterion. The most commonly used suchmathematical criterion is a least-squares criterion. In this case, forthis criterion, the 2D features observed in the first collection of 2Dscan sets are aligned so as to minimize the sum of squares of residualerrors in the matching of the features.

In the element 1725, the 3D scanner, while in the second registrationposition, obtains 3D coordinates of a second collection of points on theobject. In general, the first collection of points measured by the 3Dscanner at the first registration position are not exactly the samepoints as the second collection of points measured by the 3D scanner atthe second registration position. However, the points provide theinformation needed to identify the target features, which might benatural features or artificial features.

In the element 1730, the measuring device, while moving from the secondregistration position to a third registration position, determines acorrespondence among registration targets seen in the first collectionof 3D points observed at the first registration position and theregistration targets seen in the second collection of 3D points observedat the second registration position. This registration is based at leastin part on the first translation value, the second translation value,and the first rotation value, which provide the initial conditions fromwhich the mathematical matching of 3D feature is carried out.

In the element 1735, the first translation value, the second translationvalue, and the first rotation value are stored.

Terms such as processor, controller, computer, DSP, FPGA are understoodin this document to mean a computing device that may be located withinan instrument, distributed in multiple elements throughout aninstrument, or placed external to an instrument.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

What is claimed is:
 1. A method for measuring and registeringthree-dimensional (3D) coordinates comprising: fixedly locating ameasuring device in a first registration position, the measuring deviceincluding a 3D scanner on a moveable platform; obtaining with the 3Dscanner, while in the first registration position, 3D coordinates of afirst collection of points on an object, the 3D scanner configured todetermine the 3D coordinates of the first collection of points byprojecting a beam of light onto the object and obtaining for each pointin the first collection of points a distance and two angles in response,the distance based at least in part on a speed of light in air;obtaining by the 3D scanner a first plurality of 2D scan sets while themeasuring device moves from the first registration position to a secondregistration position, each of the first plurality of 2D scan sets beinga set of 2D coordinates of points on the object, each of the firstplurality of 2D scan sets being collected by the 3D scanner at adifferent position relative to the first registration position;determining for the measuring device a first translation valuecorresponding to a first translation direction, a second translationvalue corresponding to a second translation direction, and a firstrotation value corresponding to a first orientational axis, wherein thefirst translation value, the second translation value, and the firstrotation value are determined based at least in part on a fitting of thefirst plurality of 2D scan sets according to a first mathematicalcriterion; obtaining with the 3D scanner, while in the secondregistration position, 3D coordinates of a second collection of pointson the object; determining by the measuring device, while the measuringdevice moves from the second registration position to a thirdregistration position, a correspondence among registration targetspresent in both the first collection of points and the second collectionof points, the correspondence based at least in part on the firsttranslation value, the second translation value, and the first rotationvalue; and storing the first translation value, the second translationvalue, and the first rotation value.
 2. The method of claim 1 furthercomprising: determining 3D coordinates of a first registered 3Dcollection of points based at least in part on a second mathematicalcriterion, the correspondence among the registration targets present inboth the first collection of points and the second collection of points,the 3D coordinates of the first collection of points, and the 3Dcoordinates of the second collection of points.
 3. The method of claim 1wherein, in fixedly locating a measuring device in a first registrationposition, the moveable platform includes motorized wheels configured tomove under computer control.
 4. The method of claim 1 wherein, inobtaining with the 3D scanner, while in the second registrationposition, 3D coordinates of a second collection of points on the object,the measuring device is further configured to respond to a stoppingsignal to cause the 3D scanner to automatically start measurement of thesecond collection of points.
 5. The method of claim 1 wherein, inobtaining by the 3D scanner a first plurality of 2D scan sets while themeasuring device moves from the first registration position to a secondregistration position, the 2D scan sets are obtained by the 3D scannerby a projecting the beam of light in a horizontal plane onto the object.6. The method of claim 1 wherein, in obtaining by the 3D scanner a firstplurality of 2D scan sets while the measuring device moves from thefirst registration position to a second registration position, adistance moved between the first registration position and the secondregistration position is based at least in part on one of the firstplurality of 2D scan sets.
 7. The method of claim 1 wherein, indetermining by the measuring device, while the measuring device movesfrom the second registration position to a third registration position,a correspondence among registration targets present in both the firstcollection of points and the second collection of points, the measuringdevice further determines a quality of the correspondence.
 8. The methodof claim 7 wherein, in determining by the measuring device, while themeasuring device moves from the second registration position to a thirdregistration position, a correspondence among registration targetspresent in both the first collection of points and the second collectionof points, the measuring device provides a notification when the qualityof the correspondence is below a quality threshold.
 9. The method ofclaim 2 wherein, in determining by the measuring device, while themeasuring device moves from the second registration position to a thirdregistration position, a correspondence among registration targetspresent in both the first collection of points and the second collectionof points, the measuring device moves to a revised second registrationposition, the revised second registration position being closer to thefirst registration position than the second registration position. 10.The method of claim 1 wherein, in determining by the measuring device,while the measuring device moves from the second registration positionto a third registration position, a correspondence among registrationtargets present in both the first collection of points and the secondcollection of points, the determining is performed at least in part by acomputing device located on the measuring device.
 11. The method ofclaim 2 wherein, in determining by the measuring device, while themeasuring device moves from the second registration position to a thirdregistration position, a correspondence among registration targetspresent in both the first collection of points and the second collectionof points, the computing device receives from the 3D scanner the firstplurality of 2D scan sets, the 3D coordinates of a first collection ofpoints, and the 3D coordinates of the second collection of points. 12.The method of claim 2 wherein, in determining 3D coordinates of a firstregistered 3D collection of points based at least in part on a secondmathematical criterion, the determining is performed at least in part byan external computing device not a part of the measuring device.
 13. Themethod of claim 2 further including obtaining by the 3D scanner a secondplurality of 2D scan sets while the measuring device moves from thesecond registration position to a third registration position, each ofthe second plurality of 2D scan sets being collected by the 3D scannerat a different position relative to the second registration position.14. The method of claim 13 further including obtaining with the 3Dscanner, while in the third registration position, 3D coordinates of athird collection of points on the object.
 15. The method of claim 14further including determining by the measuring device a correspondenceamong registration targets present in both the second collection ofpoints and the third collection of points, the determined correspondencebased at least in part on the second plurality of 2D scan sets, the 3Dcoordinates of the second collection of points on the object, and the 3Dcoordinates of the third collection of points on the object.
 16. Themethod of claim 15 further including determining 3D coordinates of asecond registered 3D collection of points based at least in part on thedetermined correspondence among the registration targets present in boththe second collection of points and the third collection of points, the3D coordinates of the second collection of points, and the 3Dcoordinates of the second collection of points.